Clutch ball ramp actuator with drive and coast apply

ABSTRACT

A first ball ramp actuator having a control ring acting with an activation ring to supply an axial clutch clamping force in a vehicle driving mode and a second ball ramp actuator using the control ring acting with a clutch pressure plate to supply an axial clutch clamping force in a vehicle coast mode where one side of a one-way clutch is attached to the control ring and another side is attached to a support bracket that is frictionally coupled to a transmission input shaft to maintain an energized rotational relationship with the activation ring when in the coast mode.

RELATED APPLICATIONS

This application is related to application U.S. Ser. No. 08/189,342 andfiled on Jan. 31, 1994, and application U.S. Ser. No. 08/165,684 filedon Dec. 13, 1993, both assigned to the same assignee, Eaton Corporation,as this application.

BACKGROUND OF THE INVENTION

The present invention relates to a vehicle driveline clutch and moreparticularly, to a driveline clutch where a friction disc is clamped toan engine flywheel using a ball ramp actuator where a one-way clutch isused to provide drive and coast driveline clutch lock-up.

Driveline clutches commonly use a plurality of springs to clamp afriction disc to an engine flywheel. The springs are disposed within apressure plate assembly which is bolted to the flywheel. A mechanicallinkage that controls the pressure plate spring mechanism is displacedby the operator to control the lock-up and release of the clutch.

Efforts to automate the operation of the clutch using electronics arecurrently underway. It is known to use an electromechanical or hydraulicactuator connected to the mechanical linkage to, in essence, replace theoperator for more accurate clutch operation during transmissionshifting. Using such an actuator, the mechanical linkage is moved inresponse to an electrical control signal generated by a centralmicroprocessor used to process a variety of vehicle sensor inputs andother operating conditions to determine when and in what manner thedriveline clutch should be activated, or deactivated.

The use of a ball ramp actuator to load a clutch pack in a vehicledriveline differential is known. U.S. Pat. Nos. 5,092,825 and 4,805,486,the disclosures of which are hereby incorporated by reference, discloselimited slip differentials where a clutch pack is loaded in response tothe activation of a ball ramp actuator initiated by rotation of a servomotor or a solenoid driven brake shoe on an activating ring. Theadvantage of the ball ramp mechanism over other actuators is that itconverts rotary motion into axial motion with a very high forceamplification, often 100:1 or greater. A ball ramp actuator has alsobeen utilized in a vehicle transmission to engage and disengage gearsetsby loading a gear clutch pack in response to a signal as disclosed inU.S. Pat. No. 5,078,249 the disclosure of which is hereby incorporatedby reference.

In both of these applications, one side of the ball ramp actuator,commonly called a control ring, reacts against case ground through theforce induced by an electromagnetic field generated by a coil or isrotated by an electric motor relative to case ground. To generategreater clamping forces, the electrical current supplied to the coil ormotor is increased thereby increasing the reaction of the control ringto case ground which rotates the control ring relative to an activationring thereby causing rolling elements to engage ramps in the control andactivation ring which increase the axial movement and clamping force onthe clutch pack.

One problem with the use of a ball ramp actuator to supply the clutchclamping force is that the mechanics of prior art unidirectional ballramp mechanisms result in a loss of clamping force when the vehicle isin a coast mode. Once the engine power is reduced and the driveline isactually overrunning the engine (coast mode), the prior art ball rampactuator with single ramp unidirectional actuation will disengage theclutch thereby eliminating the potential for engine braking of thevehicle.

In other words, this type of prior art ball ramp actuated clutch using aball ramp having only a single ramp angle, will cause the clutch todisengage when the engine is not supplying rotational energy into thetransmission when the vehicle is coasting. When coasting, the flywheelis no longer supplying rotational energy to either the transmission orthe ball ramp actuator. In this circumstance, the relative rotation ofthe activation ring and control ring has been reversed such that theball ramp axial displacement is collapsed thereby allowing the pressureplate to pull away from the clutch disc. The result is that the engineis disengaged from the transmission and any engine braking effort iseliminated.

The ball ramp actuator comprises a plurality of roller elements, acontrol ring and an opposed activation ring where the activation ringand the control ring define at least three opposed single ramp surfacesformed as circumferential semi-circular grooves, each pair of opposedgrooves containing one roller element. A plurality of thrust balls (orother type of thrust bearing) are interposed between the control ringand a housing member, rotating with and connected to the input membersuch as a flywheel. An electromagnetic coil is disposed adjacent to oneelement of a control clutch so as to induce a magnetic field that loadsthe control clutch which in turn applies a force on the control ring ofthe ball ramp actuator. The control clutch can be similar to thosecommonly used for vehicle air conditioning compressors.

SUMMARY OF THE INVENTION

As an alternative, reference is made to an efficient, quick acting ballramp clutch actuator as disclosed in patent application Ser. No.08/165,684 filed on Dec. 13, 1993 having an attorney docket number93-RTRN-456. The ball ramp mechanism in the Ser. No. 08/165,684disclosure has dual angle ramps where the clutch is locked in both thedrive and coast mode of vehicle operation. That invention also providesfor a ball ramp actuator for an electronically controlled clutch such asmight be used in a motor vehicle. The present invention uses a ball rampactuator having single angle ramps which allow the outside diameter ofthe ball ramp actuator to be significantly reduced.

The present invention is characterized by a flywheel and a transmissioninput shaft being coupled through a control ring having single directionvariable depth grooves (ramps) and an activation ring having singledirection variable depth grooves at least partially opposed to those ofthe control ring of a ball ramp actuator where the activation ring isprevented from counterrotating by a one-way clutch. An electromagneticcoil is used to activate a control clutch which frictionally couples thecontrol ring to the transmission input shaft. The ball ramp actuatorprovides a clamping force on the clutch friction disc whose amplitudeimmediately increases with the differential speed between the input(flywheel) and output (transmission) shafts without complex electronicintervention using the coil. Upon lock-up between the flywheel and thetransmission input shaft, the parasitic energy loss is minimized sincethere is no slippage in the control clutch which is connected to thetransmission input shaft as opposed to case ground as found in prior artsystems.

One provision of the present invention is to prevent a ball rampactuated clutch from disengaging when the input torque is reversed.

Another provision of the present invention is to prevent a ball rampactuated clutch from disengaging by locking the rotational orientationbetween a control ring arid an activation ring using a one-way clutchwhen the driveline input is reversed.

Still another provision of the present invention is to prevent a firstball ramp mechanism from disengaging when the driveline torque isreversed by locking the rotational orientation between a control ringand an activation ring and providing a ball ramp mechanism between thecontrol ring and a pressure plate which energizes in a directionopposite to the first ball ramp mechanism.

The present invention makes use of a one-way clutch defined for purposesof this application as any mechanism which permits rotation of anelement in one direction and prevents substantial rotation in anopposite direction. The purpose of the one-way clutch as used in theball ramp actuator of the present invention is to hold the actuationring in a fixed position relative to the control ring so as to maintainthe existing clamping force on the clutch plate when the input torque isreversed such as in a vehicle coast mode. Using a one-way clutch of thepresent invention allows a clutch having a unidirectional ball rampactuator with single angle ramps (grooves) (which only applies aclamping load when the control ring is rotated in one direction relativeto the activation ring) to apply a clutch clamping force when the engineis driving or being driven. A bidirectional ball ramp actuator such asthat disclosed in U.S. Ser. No. 08/165,684 has dual angle ramps whichoperate in either direction of rotation and a one-way clutch would notserve any meaningful purpose other than prevent a momentary clutchrelease upon a vehicle drive to coast transition.

With the use of a one-way clutch acting essentially between atransmission input shaft and the actuation ring of a ball ramp actuatorhaving single angle grooves, the clamping force of a clutch disc can bemaintained as the input torque to the driveline clutch is reversed. Asecond ball ramp mechanism with reverse acting ramps can be used betweenthe actuation ring and the pressure plate: to provide an additionalclamping force upon torque reversal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of the ball ramp actuator ofthe present invention mounted to input and output members;

FIG. 2 is a front sectional view taken along line II--II of FIG. 1 ofthe activation ring, control ring and pressure plate of the ball rampactuator of the present invention:

FIG. 3 is a sectional view of FIG. 2 taken along line III--III of FIG. 2of the ball ramp actuator of the present invention with the actuator ina non-energized state;

FIG. 4 is a sectional view of FIG. 2 taken along line III--III of FIG. 2of the ball ramp actuator of the present invention with the actuator inan energized state; and

FIG. 5 is a sectional view of FIG. 2 taken along line III--III of FIG. 2of the ball ramp actuator of the present invention with both the firstand second ball ramp mechanisms energized.

DETAILED DESCRIPTION OR THE PREFERRED EMBODIMENT

Referring now to the drawings, which are not intended to limit thepresent invention, FIG. 1 is a partial cross-sectional view of the maindriveline clutch assembly of the type in which the present invention isutilized to energize a driveline clutch by supplying an axial force to apressure plate 12 which acts to clamp a clutch disc 9 to an engineflywheel 4. Most all of the elements herein described have circularperipheral edges and encircle the transmission input shaft 8 and rotateon a common axis of rotation 59. FIG. 1 shows only a portion of theclutch assembly elements which are symmetrical around the axis ofrotation 59.

The engine flywheel 4 is rotatably driven by a prime mover (not shown)such as an internal combustion engine through its crankshaft (also notshown). The crankshaft rotates the flywheel 4 which is coupled to atransmission 3 through the driveline clutch assembly of the presentinvention by the clamping action of the pressure plate 12 to the clutchdisc 9 which rotatably drives the transmission input shaft 8. A pressureplate 12 is used to clamp the clutch disc 9 which is nonrotatablyattached to the transmission input shaft 8 through engagement of aplurality of shaft splines 13 and mating clutch disc splines 11 throughattached friction pads 10 to the flywheel 4 thereby transferring therotational power from the engine to the transmission 3 and subsequentlyto the rest of the vehicle driveline.

The pressure plate 12 is typically forced toward the flywheel 4 using areaction of a plurality of high spring rate clutch springs. When theoperator wishes to disengage the clutch disc 9, a mechanical releasemechanism is activated by movement of the operator's foot and legthereby overcoming the force of the clutch springs and allowing theclutch disc to slip relative to the flywheel 4. It should be understood,that neither the clutch springs nor the mechanical release mechanism arefeatures of the present invention. Instead, a first ball ramp actuatormechanism 5A is used to axially force the pressure plate 12 toward theflywheel 4 which is controlled by clutch control electronics 15 whichcontrols most all of the transmission 3 shifting sequences.

Ball ramp mechanisms are well known in the art and have been used toload transmission gear clutches as disclosed in U.S. Pat. No. 5,078,249,the disclosure of which is hereby incorporated by reference, anddifferential clutch packs; as disclosed in U.S. Pat. No. 5,092,825, thedisclosure which is incorporated by reference. In the prior art, theball ramp control mechanism is energized through a reaction of a controlring against case ground by an electrical coil or motor. The detailedoperation of the ball ramp actuator 5 is disclosed in U.S. Pat. No.5,078,249 and U.S. Pat. No. 5,092,825.

In essence, relative motion between a control ring 16 and an activationring 18 being driven through the pressure plate 12 by the second ballramp mechanism 5B which is locked by its geometry causes one or morerolling elements 20A (which can be spherically shaped or barrel shapedin addition to other designs) to roll along a like number of opposedramps 22A and 23A formed in the control ring 16 and the activation ring18. FIG. 2 illustrates this geometry with more detail and precision,reference to which is made subsequently.

Referring once again to FIG. 1, the annular control ring 16 is axiallyloaded by the first ball ramp mechanism 5A and reacts against a thrustbearing 27 which is trapped between the control ring 16 and a mechanismsupport member 34 which is attached to the flywheel 4. The supportbearing 27 provides for axial support of the control ring 16 whileallowing for relative rotation with respect to the support member 34.

The control ring 16 is frictionally coupled to the transmission inputshaft 8 through the action of an energizing coil 30 which causes thecontrol ring 16 to be axially loaded against a friction element 28thereby completing the coupling arrangement to the transmission inputshaft 8. The coil 30 is electrically energized using a clutch controlunit 15 which in turn can be controlled by a vehicle system electroniccontrol unit (not shown). The electrical current is introduced into thecoil 30 by the clutch control unit 15 where the electrical current inthe coil 30 creates a magnetic field 36 which flows through a narrow airgap 35 through the control support 37 (specifically the magnetic section37B) through the locking ring 32 into the control ring 16 and thenreturning to the coil 30 in a circular manner. The coil 30 creates themagnetic field 36 which provides electromagnetic coupling of the controlring 16 to the locking ring 32 through the friction element 28 andcontrol support magnetic section 37B and functions to frictionallycouple the control ring 16 to the transmission input shaft 8. The coil30 is mounted to case ground through support bracket 31 which isattached to the case of the transmission 3. The narrow air gap 35 existsbetween the coil 30 and the locking ring 32 since the coil 30 isgrounded and the locking ring 32 rotates with the transmission inputshaft 8.

A control support extension section 37A (which is joined to the magneticsection 37B to form the control support 37) supports one side of aone-way clutch 38. A second side of the one-way clutch 38 is mounted tothe activation ring 18. The purpose of the one-way clutch 38 is toprevent relative rotation between the control ring 16 and the activationring 18 so as to maintain the position of the first ball ramp mechanism5A such that the coupling between the flywheel 4 and the transmissioninput shaft 8 is maintained in any vehicle operating mode such as driveor coast and in addition serves to drive the second ball ramp mechanism5B in coast mode. In this manner, the engine can act as a brake to slowthe vehicle when in a vehicle coast mode since the ball ramp actuatorremains in the energized state by operation of the one-way clutch 38. Inthe prior art, the ball ramp clutch mechanism with a one-way ramp woulddisengage the clutch whenever the rotational torque is reversed such asin the vehicle coast mode.

The one-way clutch 38 functions to lock the activation ring 18 to thecontrol support extension 37A which is connected to the magnetic section37B to form the control support 37 which is in turn rotatably supportedby the transmission input shaft 8. Bushing 39 surrounds the transmissionmain shaft 8 and serves to rotatably support the control support 37 atthe control support extension 37A. Thus, unless the coil 30 isenergized, the control support 37 is free to rotate thereby allowing theone-way clutch to rotate with the control ring 16 so that the controlring 16 and the activation ring 18 are free to assume a non-energizedrotational orientation.

In normal operation, when the engine is powering the vehicle drivelinethrough rotation of its flywheel 4 then through the ball ramp clutchassembly 2, the one-way clutch 38 is free to allow motion in onedirection between the activation ring 18 and control ring 16 whichfurther clamps the pressure plate 12. The one-way clutch 38 does notpermit the relative rotation of the control ring 18 relative to theactivation ring 16 so as to reduce the clamping force on the clutch disc9 so long as the coil 30 is energized to magnetically connect thecontrol support 37 through its magnetic section 37B to the transmissioninput shaft 8 through the locking ring 32. The clutch disc 9 is clampedbetween the pressure plate 12 and the flywheel 4 and is composed of aplurality of friction plates 10 and a spline 11 which slidingly andnonrotatably engages the transmission input shaft 8 through splines 13thereby completing the torque transfer path.

When the vehicle is in a coast mode, where the driveline is powering theengine, the; one-way clutch 38 locks the activation ring 18 to thelocking ring 32 through the control support extension 37A where the coil30, if energized, is also functioning to frictionally lock the controlring 16 to the locking ring 32, and locking ring 32 is splined to inputshaft 8 and in turn supplies coast torque to ball ramp mechanism 5B toactivate and supply a clamping force to the clutch disc 9, therebymaintaining the relative rotational orientation between the control ring16, the activation ring 18 and input shaft 8. The result is that theclamping force supplied by the control ring 18 and the activation ring16 is maintained at its current level and additional clamping isprovided whenever the vehicle goes into a coast mode such that thetransmission input shaft 8 transfers power to the engine flywheel 4.

To further clamp the clutch disc 9 between the flywheel 4 and thepressure plate 12 in the coast mode where the driveline is rotating theengine, the second ball ramp mechanism 5B is energized in the oppositerotational direction to the first ball ramp mechanism 5A. The secondball ramp mechanism 5B does not provide for relative movement betweenthe activation ring 18 and the pressure plate 12 when the engine ispowering the vehicle. When the torque transfer is reversed in thevehicle coast mode, the activation rings rotate through a small anglerelative to the pressure plate 12 thereby causing a plurality of rollingelements 26A, 26B and 26C to travel along opposing ramps 24A and 25A,24B and 25B, and 24C and 25C respectively which causes the second ballramp mechanism 5B to expand axially thereby supply additional clampingforce to the clutch disc 9.

The pressure plate 12 is nonrotatably coupled to the engine flywheel 4by way of a retaining bolt 40 where the pressure plate 12 is slidablyconnected to the retaining bolt 40 and is forced away from the flywheel4 by the return spring 42. In this manner, when the first and secondball ramp mechanisms 5A and 5B are in a non-energized state, the returnspring 42 forces the pressure plate 12 away from the flywheel 4 therebyreleasing the clutch disc 9 so that the engine flywheel 4 can freelyrotate relative to the transmission input shaft 8 and no torque istransferred through the clutch assembly. A bellhousing 6 surrounds theflywheel 4 and the ball ramp clutch assembly 2 where it is commonpractice to bolt the transmission 3 to the bellhousing 6.

Now referring to FIGS. 2, 3, 4 and 5, the control ring 16 is shaped in adisc configuration surrounding the transmission input shaft 8 androtating about a common axis of rotation 59. The control ring 16 has aplurality of radial grooves 22A, 22B and 22C formed therein which varyin axial depth along their length. Grooves 22A, 22B and 22C are shown inmore detail by reference to FIGS. 3, 4 and 5 and constrain sphericalelements 20A, 20B and 20C. In a similar manner, activation ring 18contains a like number and orientation of circumferentially extending(at a constant radius to the axis of rotation 59) grooves directlyopposing the grooves in the control ring. Specifically, control ringgroove 22A is partially opposed to activation ring groove 23A when theball ramp mechanism 5 is in a non-energized state as shown in FIG. 3 anddirectly opposes the activation ring groove 23A when in a fullyenergized state (not shown).

Upon relative rotational motion between the control ring 16 and theactivation ring 18, the spherical element 20A rolls relative to thecontrol ring groove 22A and activation control ring groove 23A where thevariable depth of the grooves 22A and 23A as shown in FIG. 4 provide foran axial motion that tends to separate the control ring 16 from theactivation ring 18. This axial motion is shown by reference to theseparation gap 44. In the non-energized state as shown in FIG. 3, theseparation gap 44 is relatively narrow and after relative rotation ofthe control ring 16 and the activation ring 18 to the energized stateshown in FIG. 4, the separation gap is significantly wider as discussedinfra.

The axial motion supplied by the first and second ball ramp mechanisms5A and 5B are used to axially move the pressure plate 12 toward theflywheel 4 thereby supplying a clamping force on the clutch disc 9. Thismotion is more clearly exemplified in FIGS. 3, 4 and 5 and referencethereto will now be made. FIGS. 3, 4 and 5 are sectional views of FIG. 2taken along line III--III of the control ring 16 and the activation ring18 and the pressure plate 12 of the present invention. FIG. 3 shows thefirst ball ramp mechanism 5A in a non-energized state where thespherical element 20A is located at the deepest depth of the controlring groove 22A and the deepest portion of the activation ring groove23A thereby establishing a relatively narrow separation gap 44 betweenthe control ring 16 and the activation ring 18. Also shown is the secondball ramp mechanism 5B between the activation ring 18 and the pressureplate 12 where spherical element 26A is located in the deepest portionof the activation ring groove 24A and the deepest portion of thepressure plate groove 25A thereby establishing a relatively narrowseparation gap 46.

FIG. 4 illustrates the relationship between the control ring 16, theactivation ring 18 and the pressure plate 12 when the first ball rampmechanism 5A is energized by supplying electrical current to the coil 30from the clutch control unit 15 and the engine is supplying torque tothe driveline. The magnetic interaction between the coil 30, the lockingring 32, the control support 37 and the control ring 16 causes thefriction element 28 to contact and frictionally connect the control ring16 to the transmission input shaft 8. Thus, since the pressure plate 12is rotating and attached to the engine flywheel 4, and ball rampmechanism 5B cannot rotate in an engine drive direction, if there isrelative rotational speed differences between the engine flywheel 4 andthe transmission input shaft 8 there is relative rotational motioninduced between the pressure plate 12 and the control ring 16. Thisrelative rotational motion causes the control ring 16 to rotate relativeto the activation ring 18 to establish a geometrical relationship asshown in FIG. 4. The separation gap 44 is significantly increased ascompared to the non-energized state of FIG. 3 while the separation gap46 remains the same as in the, non-energized state in FIG. 3 since thesecond ball ramp mechanism 5B is locked until the torque is reversed.The spherical element 20A has rolled along both the control ring groove22A and the activation ring groove 23A to an intermediate depth of thegrooves 22A and 23A thereby further separating the control ring 16 fromthe activation ring 18 and providing axial movement from the supportmember 34 as shown by the increase in the separation gap 44 which istransferred to the pressure plate 12 for clamping of the clutch disc 9to the flywheel 4.

To provide engine braking effect in the vehicle coast operating mode,the coil 30 remains energized and the one-way clutch 38 operates againstthe control support 37 to prevent the first ball ramp mechanism 5A fromreleasing. The second ball ramp mechanism 5B has a reversed directionramp orientation between the activation ring 18 and the pressure plate12 so that reverse torque transfer results in activation of the secondball ramp actuator 5B thereby increasing the clamping force of thepressure plate 12 on the clutch disc 9. Referring to FIG. 5, sphericalelement 26A has rolled along activation ring groove 24A and pressureplate groove 25A (also referred to as plate grooves) to an intermediatedepth of the grooves 24A and 25A thereby increasing the separation gap46 as compared to that shown in FIGS. 3 and 4. The result is thatadditional axial motion is applied to the pressure plate 12 relative tothe engine flywheel 4 and the support member 34 which clamps the clutchdisc 9 between the pressure plate 12 and the engine flywheel 4 therebyfrictionally connecting the flywheel 4 to the transmission input shaft8.

According to the present invention, once the clutch assembly 2 isengaged by action of either the first ball ramp actuator 5A or thesecond ball ramp actuator 5B, the engine can supply power to the vehicledriveline thereby propelling the vehicle. When it is no longer desirableto increase the speed of the vehicle by supplying power from the engineto the driveline, the engine power is decreased and the engine can actas a brake to the vehicle by reversing the flow of rotational power fromthe engine to the driveline to one flowing from the driveline to tileengine. The one-way clutch 38 serves to maintain the relative rotationalposition of the activation ring 18 relative to the control ring 16 andthe pressure plate 12 thereby maintaining the clamping force between thepressure plate 12 and the flywheel 4 to maintain the frictional couplingbetween the transmission input shaft 8 and the flywheel 4 so that thedriveline can supply rotational power to the engine which, if the enginethrottle is closed, will tend to brake the vehicle. An additionalclamping force can be supplied by a second ball ramp mechanism 5B placedbetween the activation ring 18 and the pressure plate 12 designed toenergize when the torque flow reverses as during vehicle coasting.

This invention has been described in great detail, sufficient to enableone skilled in the art to make and use the same. Various alterations andmodifications of the invention will occur to those skilled in the artupon the reading and understanding of the foregoing specification, andit is intended to include all such alterations and modifications as partof the invention, insofar as they come within the scope of the intendedclaims.

We claim:
 1. A ball ramp mechanism for coupling two rotating elementscomprising:an input element driven by a prime mover and rotating aboutan axis of rotation; an output element having an axis of rotationcoaxial with said axis of rotation of said input element for rotating anoutput device; a first ball ramp actuator for generating an axialmovement comprising; an annular control ring adapted to be magneticallycoupled to said output element and to rotate therewith, said controlring having at least two circumferential control ramps formed in a firstface of said control ring, said control ramps varying in axial depth, anequivalent number of rolling elements one occupying each of said ramps,an activation ring having an axis of rotation along said axis ofrotation of said control ring, said activation ring having at least twoactivation ramps substantially identical in number, shape and .[.adial.]. .Iadd.radial .Iaddend.position to said control ramps in saidcontrol ring where said activation ramps at least partially oppose saidcontrol ramps and where each of said rolling elements is trapped betweensaid activation ramp and a respective at least partially opposed controlramp, said control ring axially and rotationally movably disposedrelative to said activation ring; a second ball ramp actuator forgenerating an axial movement wherein said activation ring has aplurality of opposite acting circumferential activation coast rampsformed in a second face of said activation ring and substantiallyidentical partially opposed plate ramps formed in a pressure plate wheresaid plate ramps and said coast ramps have a variable depth with anequivalent number of rolling elements one occupying each pair ofpartially opposed ramps which roll along said coast ramps and said plateramps and operate to axially displace the activation ring from thepressure plate when rotated in a relative direction opposite to thedirection of rotation causing axial displacement of said first ball rampactuator; coupling means for rotatably joining said input element tosaid output element where said coupling means varies the degree ofrotational .[.Coupling.]. .Iadd.coupling .Iaddend.between said inputelement and said output element according to the axial position of saidcontrol ring relative to said activation ring, said coupling meanscomprising: a flywheel attached to said input element having a frictionsurface; a clutch disc having a first friction surface for frictionallyreacting against said flywheel friction surface and a second frictionsurface; said pressure plate having a friction surface for frictionallyreacting against said clutch disc second friction surface where saidpressure plate is nonrotatably connected to said flywheel; a lockingring nonrotatably attached to said output element; a control supportelement disposed between said control ring and said locking ring, saidcontrol support rotatably supported by said output element; a coil forcreating a magnetic field in said locking ring and said control ring andsaid control support thereby magnetically joining said control ring tosaid output element, .[.Said.]. .Iadd.said .Iaddend.coil beingelectrically energized by a clutch control unit where said activationring rotates with said input element and said control ring rotates withsaid output element according to said control means; control clutchmeans for limiting the rotation of said activation ring relative to saidcontrol ring when said coil is energized, said clutch means attached tosaid control support and to said activation ring.
 2. The ball rampmechanism of claim 1, wherein said input element comprises a flywheeland where said output element comprises a transmission input shaft, saidflywheel rotatably joined to said coupling means.
 3. The ball rampmechanism of claim 1, wherein said coil is attached to a transmissioncase.
 4. The ball ramp mechanism of claim 1, wherein a friction pad ismounted to said control support for frictionally contacting said controlring and supplying a rotational torque thereto.
 5. The ball rampmechanism of claim 1, wherein said rolling elements are sphericallyshaped.
 6. A driveline clutch for coupling a flywheel to a transmissioninput shaft comprising:a flywheel rotated about an axis of rotation by aprime mover; a driveline transmission having an input shaft and ahousing; a clutch disc splined to said input shaft radially extendingfrom said input shaft and having friction material on a first surfaceand a second surface where said first surface frictionally engages saidflywheel; a pressure plate encircling said input shaft having a firstsurface for frictionally engaging said second surface of said clutchdisc; a first ball ramp mechanism for moving said pressure plate towardsaid clutch disc and said flywheel thereby causing said clutch disc tobe clamped therebetween comprising; an activation ring encircling saidinput shaft, said activation ring being connected to said pressure platewhere axial movement of said activation ring results in axial movementof said pressure plate; a control ring encircling said input shaft anddisposed adjacent to said activation ring, said control ring and saidactivation ring having opposed faces provided with circumferentiallyextending grooves, arranged in at least three opposed pairs, saidgrooves having portions of varying depth, and rolling members disposedone in each opposed pair of grooves, the grooves on said activation ringand said adjacent control ring being arranged so that relative angularmovement of said activation ring and said control ring in a drivedirection, from a starting position thereof, causes axial movement ofsaid activation ring away from said control ring and operating toaxially displace said adjacent pressure plate; a second ball rampmechanism for moving said pressure plate toward said clutch disc andsaid flywheel thereby causing said clutch disc to be clampedtherebetween disposed between said pressure plate and said activationring, said pressure plate and said activation ring having opposed facesprovided with circumferentially extending grooves arranged in at leastthree partially opposed pairs, said grooves having portions of varyingdepth; and rolling members disposed one in each opposed pair of grooves,the grooves on said pressure plate and said adjacent activation ringbeing arranged so that relative angular movement of said activation ringand said pressure plate in an opposite drive direction, from a startingposition thereof, causes axial movement of said pressure plate towardsaid clutch disc; bearing means operative to absorb axial thrust loadsfrom said control ring, said bearing means reacting against saidflywheel through a support member; a locking ring nonrotatably attachedto said transmission input shaft; a control clutch having a firstfriction element attached to said control ring and a second frictionelement nonrotatably attached to said input shaft where uponapplication, said control clutch frictionally couples said control ringto said input shaft; a control support having a magnetic sectiondisposed between said control ring and said locking ring, said controlsupport having a control support extension section rotatably supportedby said input shaft; a one-way clutch having one side attached to saidactivation ring and a second side attached to said control supportoriented to prevent said activation ring from rotating with respect tosaid control ring in a direction to release said ball ramp mechanism; acoil for inducing a magnetic field in said control ring, said controlsupport and said locking ring thereby magnetically coupling said controlring to said transmission input shaft.
 7. The driveline clutch of claim6, wherein said control support has a friction element attached to saidmagnetic section disposed to frictionally engage said control ring uponenergization of said coil.
 8. The driveline clutch of claim 6, whereinsaid rolling members are spherical.
 9. A driveline clutch employing aball ramp actuator comprising:an input shaft rotatable about an axis ofrotation; an output shaft rotating about said axis of rotation; aflywheel having a friction surface, said flywheel attached to said inputshaft and rotating therewith about said axis of rotation; a clutch dischaving a first friction surface and a second friction surface rotatableabout said axis of rotation of said input shaft, said first frictionsurface opposed to said flywheel friction surface; a pressure platehaving a friction surface opposed to said second friction surface ofsaid clutch disc, said pressure plate rotatable about said axis ofrotation and nonrotatably connected to said flywheel; a first ball rampactuator for axially displacing said pressure plate toward saidflywheel, said first ball ramp actuator comprising a control ring and anactivation ring having opposed faces provided with circumferentiallyextending grooves, arranged as at least three opposed pairs of grooves,including portions of varying depth, and rolling members disposed one ineach opposed pair of grooves, said grooves on said activation ring andsaid adjacent control ring being arranged so that relative angularmovement of said activation ring and said control ring in a firstdirection, from a starting position thereof, causes axial movement ofsaid activation ring away from said control ring to move said pressureplate toward said flywheel thereby clamping said clutch disc, saidactuation plate being linked to said pressure plate, said coupling ringand said actuation ring being rotatable about said axis of rotation; asecond ball ramp actuator for axially displacing said pressure platetoward said flywheel, said second ball ramp actuator comprising saidactivation ring and said pressure plate having opposed faces providedwith circumferentially extending grooves, arranged as at least threeopposed pairs of grooves, including portions of varying depth, androlling members disposed one in each opposed pair of grooves, saidgrooves on said activation ring and said adjacent pressure plate beingarranged so that relative angular movement of said activation ring andsaid pressure plate in a second direction opposite to said firstdirection, from a starting position thereof, causes axial movement ofsaid pressure plate away from said activation ring to move said pressureplate toward said flywheel thereby clamping said clutch disc; a lockingring nonrotatably attached to said output shaft; a coil for inducing amagnetic field in said locking ring; a one-way clutch having one sidereleasably coupled to said transmission input shaft through said lockingring and a second side attached to said activation ring for preventingrelative rotation of said activation ring and said control ring whensaid coil is energized; coupling means for linking said output shaft tosaid control ring.
 10. The driveline clutch of claim 9, wherein saidcoil is electrically energized by an electronic clutch control unit. 11.The driveline clutch of claim 9, wherein said coupling means iscomprised of a control support having a magnetic section disposedbetween said control ring and said locking ring and an extension sectionrotatably attached to said transmission input shaft where said magneticsection frictionally engages said locking ring and rotates therewithwhen said coil is electrically energized.
 12. The driveline clutch ofclaim 11, wherein a friction disc is attached to said magnetic sectionwhere said friction disc contacts and frictionally engages said controlring when said coil is electrically energized.